20mm of front rise plus 30mm of rear fall means the subject is quite a bit higher than the camera. Not an unusual situation.
A bit over 20mm of front shift means the subject is to the right of the camera and either the camera can't be moved to the right, or there's something directly in front of the camera that you want to "shoot around." Front shift is one way to have a mirror in or near the center of the frame without the camera showing up in the mirror. Although you can, in theory, just scoot the tripod a bit left or right most of the time, it can be more convenient or precise to use shift if you find you want just a wee bit of change in composition.
12 degrees of front downward tilt means the subject is not parallel to the film plane, but the photographer wants it to be in focus (or they're using the annoyingly-inaccurately-named "tilt/shift" effect to throw a subject selectively out of focus, which is just tilt, not shift!) Scheimpflug can be confusing stuff!
I don't know that I've used movements this extreme in the field, but I've certainly gotten close, and have used combinations of rise/fall and shift with tilt. I've rarely used tilt and swing together, as that tends to confuse the hell out of me. My Ebony is a field camera, so doesn't have quite as much range in its movements (and only has rear rise, not fall), but using movements is quite common with view cameras. I almost always use front rise or fall for every image, as it's easier to have the camera at my face and not move the tripod up or down or tilt the tripod head if my subject is higher or lower than I am.